Gentamicin Dosing for a 60 kg Female
For a 60 kg female with normal renal function, administer gentamicin 180 mg (3 mg/kg) divided every 8 hours, which equals 60 mg IV every 8 hours. 1
Standard Dosing Calculation
- The FDA-approved dosing for adults with serious infections and normal renal function is 3 mg/kg/day administered in three equal doses every 8 hours. 1
- For this 60 kg patient: 60 kg × 3 mg/kg/day = 180 mg/day total, divided into 60 mg every 8 hours 1
- The FDA label explicitly provides this calculation in its dosing table, confirming 60 mg per dose every 8 hours for a 60 kg patient 1
Target Serum Concentrations
- Peak concentrations should be measured 30-60 minutes after IM injection and maintained at 4-6 mcg/mL. 1
- Trough concentrations (measured just prior to next dose) should be kept below 2 mcg/mL to minimize toxicity. 1
- The American Heart Association recommends targeting peak levels of 3-4 μg/mL and trough <1 μg/mL for synergistic therapy in endocarditis 2
Critical Monitoring Requirements
- All patients receiving gentamicin require mandatory therapeutic drug monitoring with both peak and trough levels measured periodically during therapy. 2, 1
- Serum creatinine should be monitored at least weekly during therapy 2
- For treatment extending beyond 10 days, monitoring of renal, auditory, and vestibular functions is recommended since toxicity is more likely with prolonged treatment 1
Life-Threatening Infections
- For life-threatening infections, the FDA approves doses up to 5 mg/kg/day (100 mg every 8 hours for this 60 kg patient), but this should be reduced to 3 mg/kg/day as soon as clinically indicated 1
- Dosage adjustments should ensure prolonged levels above 12 mcg/mL are avoided 1
Special Considerations for Females
- Women have significantly higher volume of distribution (0.50 vs 0.40 L/kg) and lower peak concentrations compared to men, despite receiving similar mg/kg doses. 3
- Female sex is independently associated with lower probability of achieving target peak concentrations above 16 mg/L 3
- This patient may require closer monitoring or consideration of higher initial dosing (up to 7 mg/kg for first dose) to ensure adequate peak concentrations 4, 3
Renal Function Adjustments
- This dosing assumes normal renal function; any renal impairment requires mandatory dose reduction and extended dosing intervals. 2, 1
- For creatinine clearance <20 mL/min, two-week gentamicin regimens are contraindicated 2
- Consultation with infectious disease or nephrology is mandatory for CrCl <50 mL/min 2
Nephrotoxicity Prevention
- Concomitant nephrotoxic drugs (NSAIDs, vancomycin) significantly increase nephrotoxicity risk and should be avoided when possible. 2
- TDM targeting trough concentrations <0.5-1 mg/L has proven efficacy in reducing nephrotoxicity and is recommended for all patients receiving more than one dose 4